The development of high energy battery systems requires the compatibility of an electrolyte possessing desirable electrochemical properties with highly reactive anode materials, such as lithium, sodium and the like, and the efficient use of high energy density cathode materials, such as FeS.sub.2 and the like. The use of aqueous electrolytes is precluded in these systems since the anode materials are sufficiently active to react with water chemically. It has, therefore, been necessary, in order to realize the high energy density obtainable through use of these highly reactive anodes and high energy density cathodes, to turn to the investigation of nonaqueous electrolyte systems and more particularly to nonaqueous organic electrolyte systems.
The term "nonaqueous organic electrolyte" in the prior art refers to an electrolyte which is composed of a solute, for example, a salt or complex salt of Group I-A, Group II-A or Group III-A elements of the Periodic Table, dissolved in an appropriate nonaqueous organic solvent. Conventional solvents include propylene carbonate, ethylene carbonate or .gamma.-butyrolactone. The term "Periodic Table" as used herein refers to the Periodic Table of the Elements as set forth on the inside back cover of the Handbook of Chemistry and Physics, 48th Edition, The Chemical Rubber Co., Cleveland, Ohio, 1967-1968.
A multitude of solutes is known and recommended for use but the selection of a suitable solvent has been particularly troublesome since many of those solvents which are used to prepare electrolytes sufficiently conductive to permit effective ion migration through the solution are reactive with the highly reactive anodes described above. Most investigators in this area, in search of suitable solvents, have concentrated on aliphatic and aromatic nitrogen- and oxygen-containing compounds with some attention given to organic sulfur-, phosphorus- and arsenic-containing compounds. The results of this search have not been entirely satisfactory since many of the solvents investigated still could not be used effectively with extremely high energy density cathode materials and were sufficiently corrosive to lithium anodes to prevent efficient performance over any length of time.
U.S. Pat. No. 3,547,703 to Blomgren et al. discloses the use of a nonaqueous battery electrolyte employing a solute dissolved in ethylene glycol sulfite.
In an article appearing in Abstracts of the Third International Conference on Nonaqueous Solvents, July 5-7, 1972, Michigan State University, an abstract by H. L. Hoffman, Jr. and P. G. Sears discloses that 3-methyl-2-oxazolidone has been found to be a good nonaqueous solvent because of its ease of synthesis and purification, stability, attractive physical properties, broad dissolving power and coordinating ability. The article mainly related to the disclosure that the basic physical and chemical characteristics of 3-methyl-2-oxazolidone qualified it as a good potential nonaqueous solvent.
U.S. Pat. No. 3,871,916, filed on Apr. 22, 1974 by the same applicant as the subject invention, discloses a nonaqueous cell utilizing a highly active metal anode, a solid (CF.sub.x).sub.n cathode and a liquid organic electrolyte based on 3-methyl-2-oxazolidone in conjunction with a low viscosity cosolvent and a selected solute, while U.S. application Ser. No. 552,997, filed on Feb. 25, 1975 now U.S. Pat. No. 3,951,685 also by the same applicant as the subject invention, discloses a nonaqueous cell utilizing a highly active metal anode, a sollid CuO cathode and a liquid organic electrolyte based on 3-methyl-2-oxazolidone in conjunction with a low viscosity cosolvent and a selected solute.
While the theoretical energy, i.e., the electrical energy potentially available from a selected anode-cathode couple is relatively easy to calculate, there is a need to choose a nonaqueous electrolyte for such couple that permits the actual energy produced by an assembled battery to approach the theoretical energy. The problem usually encountered is that it is practically impossible to predict in advance how well, if at all, a nonaqueous electrolyte will function with a selected couple. Thus a cell must be considered as a unit having three parts -- a cathode, an anode and an electrolyte -- and it is to be understood that the parts of one cell are not predictably interchangeable with parts of another cell to produce an efficient and workable cell.
It is an object of the present invention to augment applicant's above-identified inventions by providing a nonaqueous cell which utilizes a highly active metal anode, a solid cathode selected from the group consisting of FeS.sub.2, Co.sub.3 O.sub.4, V.sub.2 O.sub.5, Pb.sub.3 O.sub.4, In.sub.2 S.sub.3 and CoS.sub.2, and a liquid organic electrolyte consisting essentially of 3-methyl-2-oxazolidone in combination with a low viscosity cosolvent and a solute.
It is a further object of the invention to provide an electrolyte solvent system for nonaqueous solid cathode cells, i.e., FeS.sub.2, Co.sub.3 O.sub.4, V.sub.2 O.sub.5, Pb.sub.3 O.sub.4, In.sub.2 S.sub.3 and CoS.sub.2 cathode cells, which comprises 3-methyl-2-oxazolidone in combination with at least one low viscosity cosolvent and a solute.
It is a further object of this invention to provide a nonaqueous cell which utilizes a highly active metal anode, a cathode selected from the group consisting of FeS.sub.2, Co.sub.3 O.sub.4, V.sub.2 O.sub.5, Pb.sub.3 O.sub.4, In.sub.2 S.sub.3 and CoS.sub.2, and a liquid organic electrolyte consisting essentially of 3-methyl-2-oxazolidone in combination with a low viscosity cosolvent and a solute that will yield a cathode efficiency above about 50% and preferably above about 75% during discharge as based on a drain of 1 mA/cm.sup.2 to 1.0 volt cutoff using a lithium anode cell.